Manufacturing method for biaxially oriented polyamide film for food packaging

Abstract

To provide a method for producing a biaxially oriented polyamide film excellent in impact resistance, bending pinhole resistance, and friction pinhole resistance and capable of reducing an environmental load.SOLUTION: There is provided a method for producing a biaxially oriented polyamide film for food packaging, which contains only a polyamide resin as a resin. The polyamide resin contains only 70-99 mass% of polyamide 6 and 1-30 mass% of polyamide 11 whose raw material is at least partially derived from biomass. The polyamide 6 contains, based on 100 pts.mass of the polyamide 6, 5-100 pts.mass of polyamide 6 obtained by chemical recycling and more than 0 pt.mass and 50 pts.mass or less of polyamide 6 obtained by mechanical recycling.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyamide film that has excellent impact resistance, flex pinhole resistance, and abrasion pinhole resistance, and that uses both raw materials derived from biomass (organic resources derived from living organisms such as plants) and polyamide 6 chemically recycled from waste polyamide products. The biaxially oriented polyamide film of the present invention is suitable for use as a food packaging film, etc. [Background technology]

[0002] Biaxially oriented films made of aliphatic polyamides, such as polyamide 6, have been widely used as packaging films due to their excellent impact resistance and resistance to pinholes caused by bending.

[0003] As a means of improving the above-mentioned pinhole resistance under bending, a film in which a polyamide-based elastomer is mixed with an aliphatic polyamide is known (see, for example, Patent Document 1). This film has good pinhole resistance under bending and impact resistance under low-temperature conditions, and is less likely to develop pinholes due to bending fatigue, even under low-temperature conditions. However, it has been found that the polyamide-based elastomer added during film production is subject to thermal degradation, which easily generates a degraded product called "pitting resin" at the die lip exit, causing a deterioration in the accuracy of the film thickness. Furthermore, the degraded product itself falls, resulting in defective products, which poses a problem of reducing production efficiency during continuous film production.

[0004] Pinholes are generated not only by bending but also by friction (rubbing). Methods for improving pinholes caused by bending and pinholes caused by friction are often contradictory. For example, increasing the flexibility of a film makes it less likely for pinholes to occur due to bending, but the softer the film, the more likely pinholes will occur due to friction. In response to this, a packaging laminate has been proposed that has excellent bending resistance and friction pinhole resistance by applying a surface coating agent to the outer surface of a biaxially oriented polyamide film (see, for example, Patent Document 2). However, this method is not very effective in preventing the occurrence of friction pinholes. In addition, a coating process is required.

[0005] In recent years, in order to build a recycling-oriented society, the use of biomass as an alternative to fossil fuels has been attracting attention in the materials field. Biomass is an organic compound that is photosynthesized from carbon dioxide and water, and by using it, it can be converted back into carbon dioxide and water, making it a so-called carbon-neutral raw material (the amount of carbon dioxide emitted and absorbed in the environment is the same, so the increase in carbon dioxide, a greenhouse gas, can be suppressed). Recently, the practical application of biomass plastics made from these biomass raw materials has progressed rapidly, and attempts are also being made to produce polyester, a general-purpose polymer material, from these biomass raw materials.

[0006] Furthermore, in order to reduce the amount of plastic waste generated, there is a demand for the use of recycled materials. Methods for recycling polyamide 6 include thermal recycling, in which it is incinerated and the heat energy is recovered, material recycling, in which it is melted and remolded for reuse, and chemical recycling, in which it is chemically depolymerized to return it to the raw materials of polyamide and reused in polyamide manufacturing, etc.

[0007] Of these, chemical recycling is an industrially useful recycling method because it breaks down polyamide 6 into its raw material, caprolactam, which can then be recovered and reused as a raw material for polyamide 6.

[0008] For example, Patent Document 3 discloses a recycling method in which used polyamide clothing products are collected, depolymerized to recover ε-caprolactam, which is then purified, polymerized, and melt-spun or molded into polyamide fibers or molded polyamide products. This technology enables recycling by returning collected clothing products to their raw materials and reusing them. Furthermore, by decomposing and purifying collected clothing products, high-purity, high-quality raw materials (raw monomers) can be obtained, which allows for recycling to produce high-quality polyamide 6 products and enable repeated recycling. Furthermore, the process of collecting and sorting collected clothing products is significantly reduced.

[0009] Polyamide resins recycled by the above-mentioned chemical recycling method have been used mainly as raw materials for fibers and molded products, but have not yet been put to practical use as food packaging films. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 11-254615 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-205761 [Patent Document 3] Japanese Patent Application Publication No. 7-310204 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a biaxially oriented polyamide film that is excellent in impact resistance, flex pinhole resistance, and abrasion pinhole resistance, and that can reduce the environmental load. [Means for solving the problem]

[0012] That is, the present invention comprises the following: [1] The polyamide resin contains 70 to 99 mass% of polyamide 6 and 1 to 30 mass% of a polyamide whose raw materials are at least partly derived from biomass; The biaxially stretched polyamide film, wherein the polyamide 6 contains 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling, based on 100 parts by mass of polyamide 6. [2] The biaxially stretched polyamide film according to [1], wherein the polyamide 6 contains, per 100 parts by mass of polyamide 6, polyamide 6 obtained by chemical recycling and 5 to 50 parts by mass of polyamide 6 obtained by mechanical recycling. [3] The radioactive carbon (C) relative to the total carbon in the biaxially oriented polyamide film 14 The biaxially stretched polyamide film according to [1] or [2], characterized in that the content of biomass-derived carbon as measured by ) is 1 to 15%. [4] The biaxially stretched polyamide film according to any one of [1] to [3], wherein the polyamide resin at least partly derived from biomass is at least one polyamide resin selected from the group consisting of polyamide 11, polyamide 410, polyamide 610, and polyamide 1010. [5] A biaxially oriented polyamide film according to any one of [1] to [4], wherein one or more layers are laminated on at least one side of the biaxially oriented polyamide film, the laminated layers containing 70 to 100 mass% of polyamide 6, and the polyamide 6 contains 5 to 100 mass parts of polyamide 6 obtained by chemical recycling, per 100 mass parts of polyamide 6. [6] The biaxially stretched polyamide film according to [5], wherein the polyamide 6 contains, per 100 parts by mass of polyamide 6, polyamide 6 obtained by chemical recycling and 5 to 50 parts by mass of polyamide 6 obtained by mechanical recycling. [7] The biaxially stretched polyamide film according to [5] or [6], wherein the thickness of the laminated layer is 7 to 50% of the total thickness of the film. [8] The biaxially stretched polyamide film according to any one of [1] to [7], which satisfies the following (a) and (b): (a) The number of pinhole defects is 10 or less when a twisting and bending test using a Gelbo flex tester is performed 1,000 times at a temperature of 1°C. (b) The distance to pinhole occurrence in the friction pinhole resistance test is 2900 cm or more [9] The biaxially stretched polyamide film according to any one of [1] to [8], which has a haze of 10% or less and a dynamic friction coefficient of 1.0 or less.

[10] The biaxially oriented polyamide film according to any one of [1] to [8], characterized in that the lamination strength after being attached to a polyethylene sealant film is 4.0 N / 15 mm or more.

[11] A laminated film in which a sealant film is laminated on at least one surface of the biaxially stretched polyamide film according to any one of [1] to

[10] .

[12]

[11] A packaging bag using the laminated film described in

[11] . [Effects of the Invention]

[0013] The biaxially oriented polyamide film of the present invention is primarily composed of polyamide 6 resin, and by blending it with a polyamide resin polymerized from specific biomass-derived raw materials and adopting specific film-forming conditions, it exhibits impact resistance, flex pinhole resistance, abrasion pinhole resistance, and adhesion to sealant films, and also produces a carbon-neutral polyamide film.

[0014] Furthermore, the biaxially stretched polyamide film of the present invention can be obtained with a reduced environmental impact by using or blending polyamide 6 chemically recycled from waste polyamide products.

[0015] Furthermore, according to the present invention, the biomass-derived polyamide effectively improves pinhole resistance, eliminating the need for adding a polyamide elastomer. This reduces the adhesion of degradation products to the inner surface of the die and the adhesion of resin to the die lip exit, which can be caused by the polyamide elastomer. As a result, the thickness unevenness of the film is prevented from worsening and long-term continuous production is possible. [Brief explanation of the drawings]

[0016] [Figure 1] Schematic diagram of friction pinhole resistance evaluation device DETAILED DESCRIPTION OF THE INVENTION

[0017] [Biaxially oriented polyamide film] The biaxially stretched polyamide film of the present invention contains, as polyamide resins, 70 to 99% by mass of polyamide 6 and 1 to 30% by mass of polyamide at least partly derived from biomass. The polyamide 6 further contains 5 to 100 parts by mass of polyamide 6 obtained by chemical recycling, per 100 parts by mass of polyamide 6. By containing 70% or more by mass of polyamide 6, the film can achieve excellent mechanical strength, such as impact strength, and gas barrier properties, such as oxygen barrier properties, inherent to biaxially stretched polyamide films made of polyamide 6.

[0018] The biaxially stretched polyamide film of the present invention has improved flexural pinhole resistance and abrasion pinhole resistance due to the inclusion of 1 to 30 mass% of a polyamide resin, at least a portion of which is derived from biomass. Conventionally used flexural pinhole resistance improvers, such as polyamide elastomers and polyolefin elastomers, improve flexural pinhole resistance but degrade abrasion pinhole resistance. The inclusion of a biomass-derived polyamide resin, at least a portion of which is derived from biomass, allows for the production of a biaxially stretched polyamide film that exhibits excellent flexural pinhole resistance and abrasion pinhole resistance. Furthermore, the film is carbon-neutral and has little effect on the fluctuation of terrestrial carbon dioxide.

[0019] The polyamide 6 used in the biaxially stretched polyamide film of the present invention is preferably polyamide 6 obtained by chemical recycling in an amount of 5 to 100 parts by mass, based on 100 parts by mass of the total polyamide 6. Examples of raw materials for chemical recycling include, but are not limited to, waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, and fishing nets. By using chemically recycled polyamide 6, a polyamide film can be obtained that can reduce the environmental impact.

[0020] [Polyamide 6] The polyamide 6 resin used in the present invention is usually produced by ring-opening polymerization of ε-caprolactam. The polyamide 6 resin obtained by ring-opening polymerization is usually subjected to removal of lactam monomer with hot water, followed by drying and melt-extrusion in an extruder.

[0021] The relative viscosity of the polyamide 6 resin is preferably 1.8 to 4.5, and more preferably 2.6 to 3.2. If the relative viscosity is less than 1.8, the impact strength of the film will be insufficient. If the relative viscosity is more than 4.5, the load on the extruder will increase, making it difficult to obtain an unstretched film before stretching.

[0022] The polyamide 6 used in the biaxially stretched polyamide film of the present invention may be polyamide 6 polymerized from commonly used monomers derived from fossil fuels, or polyamide 6 chemically recycled from waste polyamide 6 products such as waste plastic products, waste tire rubber, fibers, fishing nets, etc. One method for obtaining chemically recycled polyamide 6 from waste polyamide 6 products is to collect used polyamide products, depolymerize them to obtain ε-caprolactam, purify the ε-caprolactam, and then polymerize polyamide 6.

[0023] <Depolymerization conditions> In the depolymerization carried out when producing the chemically recycled polyamide 6 used in the biaxially oriented polyamide film of the present invention, the polyamide 6 product is usually depolymerized by heating. The depolymerization may or may not use a catalyst.

[0024] The depolymerization pressure may be reduced, normal pressure, or increased pressure. The depolymerization temperature is usually 100°C to 400°C, preferably 200°C to 350°C, and more preferably 220°C to 300°C. If the temperature is low, the polyamide 6 product does not melt, resulting in a slow depolymerization rate. If the temperature is high, unnecessary polyamide 6 monomer (i.e., caprolactam) may be decomposed, potentially reducing the purity of the recovered caprolactam.

[0025] When a catalyst is used in the depolymerization, an acid catalyst or a base catalyst is usually used. Examples of acid catalysts include phosphoric acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids, solid acids, and salts thereof. Examples of base catalysts include alkali hydroxides, alkali salts, alkaline earth hydroxides, alkaline earth salts, organic bases, and solid bases. Preferred examples include phosphoric acid, boric acid, organic acids, alkali hydroxides, and alkali salts. More preferred examples include phosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0026] The amount of the acid catalyst used in the depolymerization is usually 0.01 to 50% by mass, preferably 0.01 to 20% by mass, and more preferably 0.5 to 10% by mass, based on the polyamide 6 component. If the amount of catalyst used is small, the reaction rate will be slow, while if it is large, side reactions will increase and the catalyst cost will increase, which is economically disadvantageous.

[0027] The depolymerization can be carried out in the absence (dry) or presence (wet) of water. In the case of wet depolymerization, the amount of water used is 0.1 to 50 times by mass relative to the polyamide 6 product components such as fibers. Preferably, it is 0.5 to 20 times by mass, and more preferably, it is 1 to 10 times by mass. If the amount of water used is small, the reaction rate will be slow, while if it is large, the concentration of the recovered caprolactam aqueous solution will be low, which is disadvantageous in obtaining caprolactam. In the case of wet depolymerization, the produced caprolactam is distilled from the reactor together with water to obtain a recovered caprolactam aqueous solution. After the depolymerization reaction is completed, caprolactam can be extracted by vacuum distillation. Alternatively, it can be extracted continuously as the reaction proceeds. In the case of dry depolymerization, the produced caprolactam is distilled from the reactor by vacuum distillation to obtain recovered caprolactam. After the depolymerization reaction is completed, caprolactam can be extracted by vacuum distillation. Alternatively, it can be continuously removed as the reaction proceeds.

[0028] To obtain caprolactam of even higher purity, the recovered caprolactam can be combined with other purification methods, such as precision distillation of the recovered caprolactam, distillation under reduced pressure with the addition of a small amount of sodium hydroxide, treatment with activated carbon, ion exchange treatment, and recrystallization.

[0029] The biaxially oriented polyamide film of the present invention can further contain polyamide 6, which is mechanically recycled waste material generated during the manufacturing process of the biaxially oriented polyamide film.

[0030] The mechanically recycled polyamide 6 is a raw material that is made by recovering scrap materials that are generated, for example, during the production of biaxially oriented polyamide film, such as non-standard, unshippable film and offcuts (edge trims), and pelletizing them through melt extrusion or compression molding.

[0031] The proportion of mechanically recycled polyamide 6 added to the biaxially stretched polyamide film of the present invention is not particularly limited to a lower limit. The upper limit is preferably 50 parts by mass, more preferably 40 parts by mass, and even more preferably 30 parts by mass, based on 100 parts by mass of the total polyamide 6. If the proportion of mechanically recycled polyamide added exceeds the above range, the film may become more colored or have a high haze value, which may impair the appearance of the film. Alternatively, the amount of degraded material may increase during film production, which may worsen film formability.

[0032] [Polyamide resin at least partly derived from biomass raw materials] Examples of polyamide resins used in the present invention, at least a part of which is derived from biomass, include polyamide 11, polyamide 410, polyamide 610, polyamide 1010, polyamide MXD10 resin, and polyamide 11·6T copolymer resin.

[0033] Polyamide 11 is a polyamide resin having a structure in which monomers having 11 carbon atoms are bonded via amide bonds. Polyamide 11 is typically obtained using aminoundecanoic acid or undecane lactam as a monomer. Aminoundecanoic acid, in particular, is a monomer obtained from castor oil, making it desirable from the viewpoint of carbon neutrality. The structural units derived from these monomers having 11 carbon atoms preferably account for 50 mol % or more of all structural units in polyamide 11, more preferably 80 mol % or more, and even 100 mol %. Polyamide 11 is typically produced by the ring-opening polymerization of the aforementioned undecane lactam. Polyamide 11 obtained by ring-opening polymerization is typically subjected to removal of the lactam monomer with hot water, followed by drying and melt-extrusion in an extruder. The relative viscosity of polyamide 11 is preferably 1.8 to 4.5, more preferably 2.4 to 3.2. If the relative viscosity is less than 1.8, the impact strength of the film is insufficient. If it is greater than 4.5, the load on the extruder increases, making it difficult to obtain an unstretched film before stretching.

[0034] Polyamide 610 is a polyamide resin having a structure obtained by polymerizing a diamine having six carbon atoms and a dicarboxylic acid having ten carbon atoms. Hexamethylenediamine and sebacic acid are usually used. Of these, sebacic acid is a monomer obtained from castor oil, and is therefore desirable from the viewpoint of carbon neutrality. The total of the structural units derived from these monomers having six carbon atoms and the structural units derived from monomers having ten carbon atoms in PA610 preferably accounts for 50 mol % or more of all structural units, more preferably 80 mol % or more, and may even be 100 mol %.

[0035] Polyamide 1010 is a polyamide resin having a structure in which a diamine having 10 carbon atoms and a dicarboxylic acid having 10 carbon atoms are polymerized. Typically, 1,10-decanediamine (decamethylenediamine) and sebacic acid are used in polyamide 1010. Decamethylenediamine and sebacic acid are monomers obtained from castor oil, and are therefore desirable from the perspective of carbon neutrality. The total of the structural units derived from these diamines having 10 carbon atoms and the structural units derived from dicarboxylic acids having 10 carbon atoms in PA1010 is preferably 50 mol % or more, more preferably 80 mol % or more, and may even be 100 mol % of all structural units.

[0036] Polyamide 410 is a polyamide resin having a structure in which a monomer having four carbon atoms is copolymerized with a diamine having ten carbon atoms. Polyamide 410 is usually made from sebacic acid and tetramethylenediamine. From an environmental perspective, sebacic acid made from castor oil, a vegetable oil, is preferred. The sebacic acid used here is preferably obtained from castor oil from the standpoint of environmental protection (particularly from the standpoint of carbon neutrality).

[0037] In the biaxially stretched polyamide film of the present invention, the lower limit of the content of the polyamide resin at least partly derived from biomass is not particularly limited, but is preferably 1% by mass, more preferably 3% by mass or more. The upper limit of the content is 30% by mass, more preferably 20% by mass. If the content of the polyamide resin at least partly derived from biomass exceeds 30% by mass, the molten film may become unstable when cast, making it difficult to obtain a homogeneous unstretched film.

[0038] [Subsidiary materials, additives] The biaxially stretched polyamide film of the present invention may contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, anti-fogging agents, ultraviolet absorbers, dyes, pigments, etc., as needed.

[0039] <Other thermoplastic resins> The biaxially stretched polyamide film of the present invention may contain a thermoplastic resin in addition to the polyamide 6 and a polyamide resin at least partially derived from biomass, provided that the objectives of the present invention are not impaired. Examples include polyamide-based resins such as polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, polyamide 6·66 copolymer resin, and polyamide MXD6 resin. If necessary, thermoplastic resins other than polyamide-based resins, such as polyester-based polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin-based polymers such as polyethylene and polypropylene, may also be included. It is preferable that the raw materials for these thermoplastic resins are derived from biomass, as this does not affect the increase or decrease in terrestrial carbon dioxide and therefore reduces the environmental burden.

[0040] <Lubricant> The biaxially oriented polyamide film of the present invention preferably contains fine particles or an organic lubricant such as a fatty acid amide as a lubricant to improve the slipperiness and make it easier to handle. By improving the slipperiness of the biaxially oriented polyamide film of the present invention, it is also effective in reducing breakage of packaging bags due to friction.

[0041] The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, and zeolite, and polymeric organic fine particles such as acrylic and polystyrene fine particles. From the viewpoints of transparency and slipperiness, it is preferable to use silica fine particles. The average particle diameter of the fine particles is preferably 0.5 to 5.0 μm, and more preferably 1.0 to 3.0 μm. If the average particle diameter is less than 0.5 μm, a large amount of addition is required to obtain good slipperiness. On the other hand, if the average particle diameter exceeds 5.0 μm, the surface roughness of the film tends to become too large, resulting in a poor appearance.

[0042] When the silica fine particles are used, the pore volume of the silica is preferably in the range of 0.5 to 2.0 ml / g, more preferably 0.8 to 1.6 ml / g. If the pore volume is less than 0.5 ml / g, voids are likely to occur, resulting in poor film transparency, while if the pore volume exceeds 2.0 ml / g, the fine particles tend to be less likely to form protrusions on the surface.

[0043] The biaxially stretched polyamide film of the present invention may contain a fatty acid amide and / or a fatty acid bisamide to improve slipperiness. Examples of the fatty acid amide and / or fatty acid bisamide include erucamide, stearamide, ethylene bisstearamide, ethylene bisbehenamide, and ethylene bisoleamide. The content of fatty acid amide and / or fatty acid bisamide in the biaxially stretched polyamide film of the present invention is preferably 0.01 to 0.40% by mass, more preferably 0.05 to 0.30% by mass. If the content of fatty acid amide and / or fatty acid bisamide is less than the above range, the slip properties tend to be poor. On the other hand, if it exceeds the above range, the wettability tends to be poor.

[0044] To improve the slipperiness of the biaxially stretched polyamide film of the present invention, polyamide resins such as polyamide MXD6 resin, polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, and polyamide 6·66 copolymer resin can be added. Polyamide MXD6 resin is particularly preferred, and it is preferable to add it in an amount of 1 to 10 mass %.

[0045] <Antioxidants> The biaxially stretched polyamide film of the present invention may contain an antioxidant. Phenol-based antioxidants are preferred. The phenol-based antioxidant is preferably a fully hindered phenolic compound or a partially hindered phenolic compound. Examples of the phenol-based antioxidant include tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane. The inclusion of a phenol-based antioxidant improves the film-forming operability of the biaxially stretched polyamide film. In particular, when recycled films are used as raw materials, the resin is prone to thermal degradation, which can lead to operational problems in film production and increased production costs. In contrast, the inclusion of an antioxidant suppresses thermal degradation of the resin and improves operational efficiency.

[0046] [Surface layer] In the present invention, one or more surface layers made of the same or different resin compositions can be laminated on one or both sides of the biaxially stretched polyamide film. By laminating at least one surface layer, the surface properties can be improved.

[0047] The surface layer is preferably a layer made of a resin composition containing 70 to 100% by mass of polyamide 6. Preferably, the polyamide 6 content is 80% by mass or more, and more preferably 90% by mass or more. The upper limit is 100% by mass, preferably 99% by mass, and more preferably 97% by mass. By containing 70% by mass or more of polyamide 6, a biaxially oriented polyamide film having excellent mechanical strength such as impact strength and gas barrier properties for oxygen and the like can be obtained.

[0048] Furthermore, it is preferable that the polyamide 6 obtained by chemical recycling is contained in an amount of 5 to 100 parts by mass per 100 parts by mass of polyamide 6. In addition to the polyamide 6 obtained by chemical recycling, polyamide 6 obtained by mechanical recycling can be used in combination. The proportion of the polyamide 6 obtained by mechanical recycling is preferably 0 to 50 parts by mass per 100 parts by mass of polyamide 6. If the proportion of the mechanically recycled polyamide used exceeds the above range, the film may become more colored or have a high haze value, which may impair the appearance of the film. Alternatively, the amount of degraded material may increase during film production, which may deteriorate film formability.

[0049] The surface layer may contain various additives such as other thermoplastic resins, lubricants, heat stabilizers, antioxidants, antistatic agents, anti-fogging agents, ultraviolet absorbers, dyes, pigments, etc. depending on the functions to be imparted to the surface of the surface layer. When the surface layer is used on the outside of a packaging bag, it needs to be resistant to abrasion and pinholes, so it is not preferable to contain soft resins such as polyamide elastomers or polyolefin elastomers or substances that generate a large number of voids.

[0050] The surface layer may contain a thermoplastic resin other than the polyamide 6, provided that the object of the present invention is not impaired. Examples include polyamide-based resins such as polyamide MXD6 resin, polyamide 11 resin, polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, and polyamide 6·66 copolymer resin. If necessary, the surface layer may contain a thermoplastic resin other than polyamide-based resins, such as polyester-based polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin-based polymers such as polyethylene and polypropylene.

[0051] The surface layer preferably contains fine particles or an organic lubricant as a lubricant to improve the slipperiness of the film. By improving the slipperiness, the handling of the film is improved and the breakage of the packaging bag due to friction is reduced.

[0052] The fine particles can be appropriately selected from inorganic fine particles such as silica, kaolin, zeolite, etc., and polymeric organic fine particles such as acrylic and polystyrene fine particles, etc. From the viewpoints of transparency and lubricity, it is preferable to use silica fine particles.

[0053] The average particle size of the fine particles is preferably 0.5 to 5.0 μm, more preferably 1.0 to 3.0 μm. If the average particle size is less than 0.5 μm, a large amount of addition is required to obtain good slip properties. On the other hand, if the average particle size exceeds 5.0 μm, the surface roughness of the film tends to become too large, resulting in poor appearance.

[0054] When using the silica fine particles, the pore volume of the silica is preferably in the range of 0.5 to 2.0 ml / g, and more preferably 0.8 to 1.6 ml / g. If the pore volume is less than 0.5 ml / g, voids are likely to occur, resulting in poor film transparency. If the pore volume exceeds 2.0 ml / g, the fine particles tend to be less likely to form protrusions on the surface.

[0055] The organic lubricant may contain fatty acid amide and / or fatty acid bisamide. Examples of fatty acid amide and / or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, and ethylene bisoleic acid amide. The content of fatty acid amide and / or fatty acid bisamide added to the surface layer is preferably 0.01 to 0.40% by mass, and more preferably 0.05 to 0.30% by mass. If the content of fatty acid amide and / or fatty acid bisamide is less than the above range, slip properties tend to deteriorate. On the other hand, if the content exceeds the above range, wettability tends to deteriorate.

[0056] To improve the slipperiness of the film, polyamide resins other than polyamide 6, such as polyamide MXD6 resin, polyamide 11, polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, and polyamide 6·66 copolymer resin, can be added to the surface layer. Polyamide MXD6 resin is particularly preferred, and it is preferable to add it in an amount of 1 to 10% by mass. If it is less than 1% by mass, the effect of improving the slipperiness of the film is small. If it is more than 10% by mass, the effect of improving the slipperiness of the film becomes saturated. Polyamide MXD6 resin is produced by polycondensation of metaxylylenediamine and adipic acid. The relative viscosity of polyamide MXD6 is preferably 1.8 to 4.5, more preferably 2.0 to 3.2. If the relative viscosity is less than 1.8 or more than 4.5, it may be difficult to knead it with the polyamide resin in an extruder.

[0057] When adding fine particles, an organic lubricant, or a polyamide resin such as polyamide-MXD6 resin to the surface layer for the purpose of improving the slipperiness of the film, it is preferable to reduce the amount of these added to the biaxially oriented polyamide film as the base material, as this will result in a film that is excellent in both transparency and slipperiness.

[0058] To improve adhesion, the surface layer can contain a polyamide resin other than polyamide 6. In this case, copolymer polyamide resins such as polyamide 6·12 copolymer resin and polyamide 6·66 copolymer resin are preferred.

[0059] The addition of auxiliary materials and additives such as lubricants and antioxidants to the biaxially oriented polyamide film and surface layer serving as the substrate of the present invention can be carried out during resin polymerization or melt extrusion in an extruder. Alternatively, a high-concentration masterbatch can be prepared and added to the polyamide resin during film production. Such known methods can be used.

[0060] [Biaxially oriented polyamide film] The thickness of the biaxially stretched polyamide film of the present invention is not particularly limited, but when used as a packaging material, it is usually 100 μm or less, and a thickness of 5 to 50 μm is generally used, and a thickness of 8 to 30 μm is particularly used.

[0061] When one or more surface layers are laminated on at least one side of the biaxially stretched polyamide film of the present invention to form a laminate film, if the thickness of the surface layer accounts for a large proportion of the total film thickness, the pinhole resistance due to bending will decrease. The thickness of the laminated layer is preferably 7 to 50%, more preferably 7 to 30%, of the total film thickness.

[0062] The biaxially stretched polyamide film of the present invention has 10 or fewer pinhole defects when subjected to a twist flex test at a temperature of 1°C 1,000 times using a Gelbo flex tester according to the measurement method described in the Examples. The number of pinhole defects is more preferably 5 or fewer. The fewer the number of pinhole defects after the flex test, the better the pinhole resistance to flexing. If the number of pinholes is 10 or fewer, a packaging bag that is less likely to develop pinholes even when a load is applied to the packaging bag during transportation, etc., can be obtained.

[0063] Furthermore, in the biaxially stretched polyamide film of the present invention, in the friction pinhole resistance test described in the Examples, the distance until pinholes appear is 2900 cm or more, more preferably 3100 cm or more, and even more preferably 3300 cm or more. The longer the distance until pinholes appear, the better the friction pinhole resistance is, and if the distance until pinholes appear is 2900 cm or more, a packaging bag that is less likely to develop pinholes can be obtained, even if the packaging bag rubs against a cardboard box or the like during transportation.

[0064] The biaxially oriented polyamide film of the present invention is characterized by excellent properties in both the flexural pinhole resistance and the friction pinhole resistance described above. The biaxially oriented polyamide film of the present invention, which has these properties, is highly useful as a packaging film because it is less likely to develop pinholes during transportation.

[0065] The heat shrinkage of the film of the present invention at 160°C for 10 minutes is in the range of 0.6 to 3.0%, preferably 0.6 to 2.5%, in both the machine direction (hereinafter abbreviated as MD) and the width direction (hereinafter abbreviated as TD). If the heat shrinkage exceeds 3.0%, curling or shrinkage may occur when heat is applied in subsequent processes such as lamination or printing. Furthermore, the lamination strength with the sealant film may be weakened. Although it is possible to reduce the heat shrinkage to less than 0.6%, this may result in mechanical fragility. Furthermore, this is not preferred because it reduces productivity.

[0066] Since excellent impact resistance is a feature of biaxially oriented polyamide films, the impact strength of the biaxially oriented polyamide film of the present invention is preferably 0.7 J / 15 μm or more, and more preferably 0.9 J / 15 μm or more.

[0067] The haze value of the biaxially stretched polyamide film of the present invention is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. A low haze value means good transparency and gloss, so when used in packaging bags, beautiful printing is possible and commercial value is increased. Since the addition of fine particles to improve the film's slipperiness increases the haze value, when the film has two or more layers, adding fine particles only to the surface layer reduces the haze value.

[0068] The dynamic friction coefficient of the biaxially stretched polyamide film of the present invention is preferably 1.0 or less, more preferably 0.7 or less, and even more preferably 0.5 or less. A small dynamic friction coefficient of the film improves the slipperiness and makes the film easier to handle. If the dynamic friction coefficient of the film is too small, it becomes too slippery and difficult to handle, so the dynamic friction coefficient of the biaxially stretched polyamide film of the present invention is preferably 0.15 or more.

[0069] The biaxially oriented polyamide film of the present invention is radiocarbon (C 14 The content of carbon derived from biomass (also called biomass ratio) measured by the method of carbon dioxide absorption spectroscopy is preferably 1 to 15% of the total carbon in the polyamide film. 14 Since carbon dioxide is contained in the atmosphere at a constant rate (105.5pMC), plants that grow by absorbing carbon dioxide from the atmosphere, such as corn, contain 14 The content is known to be about 105.5 pMC. Also, fossil fuels contain C 14 It is also known that almost no carbon atoms are contained in the polyester. 14 By measuring the ratio of carbon derived from biomass, the ratio of carbon derived from biomass can be calculated.

[0070] The biaxially oriented polyamide film of the present invention has a laminate strength of 4.0 N / 15 mm or more after being bonded to the polyethylene sealant described in the examples. The biaxially oriented polyamide film is usually laminated with a sealant film before being processed into a packaging bag. If the laminate strength is 4.0 N / 15 mm or more, when packaging bags are produced using the biaxially oriented polyamide film of the present invention in various lamination configurations, sufficient strength of the seal portion can be obtained, resulting in a strong, tear-resistant packaging bag. To achieve a laminate strength of 4.0 N / 15 mm or more, the biaxially oriented polyamide film of the present invention can be subjected to corona treatment, coating treatment, flame treatment, etc.

[0071] [Film production method] The biaxially stretched polyamide film of the present invention can be produced by a known production method. For example, sequential biaxial stretching and simultaneous biaxial stretching are mentioned. The sequential biaxial stretching method is preferable because it can increase the film production speed and is advantageous in terms of production costs.

[0072] The method for producing the biaxially stretched polyamide film of the present invention will be described below. First, the raw material resin is melt-extruded using an extruder, extruded into a film form from a T-die, and cast onto a cooling roll to cool, thereby obtaining an unstretched film.

[0073] When producing a biaxially stretched polyamide film in which a surface layer is laminated on at least one side of a substrate film, a coextrusion method using a feed block, multi-manifold, or the like is preferred to obtain a laminated unstretched film. In addition to the coextrusion method, dry lamination, extrusion lamination, or the like can also be selected. When laminating by the coextrusion method, it is desirable to minimize the difference in melt viscosity between the polyamide resin compositions used for each layer.

[0074] The melting temperature of the resin is preferably 220 to 350°C. If it is lower than this, unmelted material may occur, resulting in defects and other poor appearance, while if it exceeds this, deterioration of the resin may be observed, resulting in a decrease in molecular weight and a deterioration in appearance. The die temperature is preferably 250 to 350°C.

[0075] The cooling roll temperature is preferably from -30 to 80°C, and more preferably from 0 to 50°C. To obtain an unstretched film by casting the film-like melt extruded from a T-die onto a rotating cooling drum and cooling it, methods such as an air knife method and an electrostatic adhesion method in which a static charge is applied are preferably used, with the latter being particularly preferred.

[0076] It is also preferable to cool the surface of the cast unstretched film opposite the cooling roll. For example, it is preferable to use a method in which a cooling liquid in a tank is brought into contact with the surface of the unstretched film opposite the cooling roll, a method in which a vaporizing liquid is applied with a spray nozzle, or a method in which a high-velocity fluid is sprayed onto the surface to cool the film. The unstretched film thus obtained is stretched biaxially to obtain the biaxially stretched polyamide film of the present invention.

[0077] The stretching method may be either a simultaneous biaxial stretching method or a sequential biaxial stretching method. In either case, multi-stage stretching such as one-stage stretching or two-stage stretching can be used as the MD stretching method. As will be described later, multi-stage MD stretching such as two-stage stretching is preferred over single-stage stretching in terms of physical properties and uniformity of physical properties in the MD and TD directions (isotropy). Roll stretching is preferred for MD stretching in the sequential biaxial stretching method.

[0078] The lower limit of the MD stretching temperature is preferably 50°C, more preferably 55°C, and even more preferably 60°C. If the temperature is less than 50°C, the resin does not soften and stretching may be difficult. The upper limit of the MD stretching temperature is preferably 120°C, more preferably 115°C, and even more preferably 110°C. If the temperature exceeds 120°C, the resin may become too soft and stable stretching may not be possible.

[0079] The lower limit of the stretching ratio in the MD direction (when stretching is performed in multiple stages, the total stretching ratio obtained by multiplying each stretching ratio) is preferably 2.2 times, more preferably 2.5 times, and even more preferably 2.8 times. If it is less than 2.2 times, the thickness accuracy in the MD direction will decrease, and the crystallinity will become too low, which may result in a decrease in impact strength. The upper limit of the stretching ratio in the MD direction is preferably 5.0 times, more preferably 4.5 times, and most preferably 4.0 times. If it exceeds 5.0 times, subsequent stretching may become difficult.

[0080] When stretching in the MD direction is performed in multiple stages, the above-mentioned stretching is possible in each stretching, but the stretching ratios must be adjusted so that the product of all MD stretching ratios is 5.0 or less. For example, in the case of two-stage stretching, the first stage stretching is preferably 1.5 to 2.1 times, and the second stage stretching is preferably 1.5 to 1.8 times.

[0081] The film stretched in the MD direction is stretched in the TD direction using a tenter, heat-set, and then relaxed (also called a relaxation treatment). The lower limit of the TD stretching temperature is preferably 50°C, more preferably 55°C, and even more preferably 60°C. If the temperature is lower than 50°C, the resin does not soften, and stretching may become difficult. The upper limit of the TD stretching temperature is preferably 190°C, more preferably 185°C, and even more preferably 180°C. If the temperature exceeds 190°C, crystallization may occur, making stretching difficult.

[0082] The lower limit of the stretching ratio in the TD direction (when stretching is performed in multiple stages, the total stretching ratio obtained by multiplying each stretching ratio) is preferably 2.8, more preferably 3.2, even more preferably 3.5, and particularly preferably 3.8. If it is less than 2.8, the thickness accuracy in the TD direction will decrease, and the crystallinity will become too low, which may result in a decrease in impact strength. The upper limit of the stretching ratio in the TD direction is preferably 5.5, more preferably 5.0, even more preferably 4.7, particularly preferably 4.5, and most preferably 4.3. If it exceeds 5.5, productivity may decrease significantly.

[0083] The selection of the heat setting temperature is an important factor in the present invention. As the heat setting temperature increases, the crystallization and orientation relaxation of the film progress, improving the impact strength and reducing the heat shrinkage rate. On the other hand, if the heat setting temperature is low, the crystallization and orientation relaxation are insufficient, making it impossible to sufficiently reduce the heat shrinkage rate. Moreover, if the heat setting temperature is too high, the resin deteriorates and the film rapidly loses its toughness, such as its impact strength.

[0084] The lower limit of the heat setting temperature is preferably 210°C, more preferably 212°C. If the heat setting temperature is too low, the heat shrinkage rate becomes too large, which tends to deteriorate the appearance after lamination and reduce the laminate strength. The upper limit of the heat setting temperature is preferably 220°C, more preferably 218°C. If the heat setting temperature is too high, the impact strength tends to decrease.

[0085] The heat setting time is preferably 0.5 to 20 seconds, and more preferably 1 to 15 seconds. The heat setting time can be adjusted appropriately by balancing the heat setting temperature and the air speed in the heat setting zone. If the heat setting conditions are too weak, crystallization and orientation relaxation will be insufficient, causing the above problems. If the heat setting conditions are too strong, the film toughness will decrease.

[0086] Relaxation treatment after heat setting is effective in controlling the heat shrinkage rate. The temperature for relaxation treatment can be selected within the range from the heat setting temperature to the glass transition temperature (Tg) of the resin, but a heat setting temperature of -10°C to Tg + 10°C is preferred. If the relaxation temperature is too high, the shrinkage rate will be too fast, which can cause distortion, and is therefore undesirable. Conversely, if the relaxation temperature is too low, relaxation treatment will not occur and the film will simply become loose, which will not reduce the heat shrinkage rate and will result in poor dimensional stability.

[0087] The lower limit of the relaxation rate in the relaxation treatment is preferably 0.5%, more preferably 1%. If it is less than 0.5%, the heat shrinkage rate may not be reduced sufficiently. The upper limit of the relaxation rate is preferably 20%, more preferably 15%, and even more preferably 10%. If it exceeds 20%, sagging may occur in the tenter, making production difficult.

[0088] Furthermore, the biaxially stretched polyamide film of the present invention can be subjected to heat treatment or humidity conditioning treatment to improve dimensional stability depending on the application. In addition, to improve the adhesion of the film surface, corona treatment, coating treatment, flame treatment, etc., or printing or vapor deposition of metals, inorganic oxides, etc., can also be performed. Vapor deposition films formed by vapor deposition are preferably aluminum vapor deposition films or vapor deposition films of silicon oxide or aluminum oxide alone or in combination. Furthermore, by coating a protective layer or the like on these vapor deposition films, oxygen barrier properties, etc. can be improved.

[0089] [Laminated films and bags] The biaxially stretched polyamide film of the present invention is laminated with a sealant film or the like to form a laminate film, which is then processed into packaging bags such as bottom-sealed bags, side-sealed bags, three-side-sealed bags, pillow bags, standing pouches, gusseted bags, square-bottom bags, etc. Examples of sealant films include unstretched linear low-density polyethylene films, unstretched polypropylene films, and ethylene-vinyl alcohol copolymer resin films.

[0090] The layer structure of the laminated film of the present invention using the biaxially oriented polyamide film of the present invention is not particularly limited as long as the biaxially oriented polyamide film of the present invention is contained in the laminated film. The film used for the laminated film may be made from either petroleum-derived or biomass-derived raw materials, but polylactic acid, polyethylene terephthalate, polybutylene succinate, polyethylene, polyethylene furanoate, etc., polymerized using biomass-derived raw materials are preferred in terms of reducing environmental impact.

[0091] Examples of layer configurations of the laminated film of the present invention include ONY / adhesive / LLDPE, ONY / adhesive / CPP, ONY / adhesive / Al / adhesive / CPP, ONY / adhesive / Al / adhesive / LLDPE, ONY / PE / Al / adhesive / LLDPE, ONY / adhesive / Al / PE / LLDPE, PET / adhesive / ONY / adhesive / LLDPE, PET / adhesive / ONY / PE / LLDPE, PET / adhesive / ONY / adhesive / Al / adhesive / LLDPE, and PET / adhesive. Al adhesive / ONY / adhesive / LLDPE, PET / adhesive / Al adhesive / ONY / PE / LLDPE, PET / PE / Al / PE / ONY / PE / LLDPE, PET / adhesive / ONY / adhesive / CPP, PET / adhesive / ONY / adhesive / Al / adhesive / CPP, PET / adhesive / Al / adhesive / ONY / adhesive / CPP, ONY / adhesive / PET / adhesive / LLDPE, ONY / adhesive / PET / PE / LLDPE, ONY / adhesive / PET / adhesive CPP, ONY / adhesive / Al / adhesive / PET / adhesive / LLDPE, ONY / adhesive / Al / v / PET / PE / LLDPE, ONY / PE / LLDPE, ONY / PE / CPP, ONY / PE / Al / PE, ONY / PE / Al / PE / LLDPE, OPP / adhesive / ONY / adhesive / LLDPE, ONY / adhesive / EVOH / adhesive / LLDPE, ONY / adhesive / EVOH / adhesive / CPP, ONY / adhesive / aluminum-deposited PET / adhesive / LLDPE, ON Examples include Y / adhesive / aluminum-vaporized PET / adhesive / ONY / adhesive / LLDPE, ONY / adhesive / aluminum-vaporized PET / PE / LLDPE, ONY / PE / aluminum-vaporized PET / PE / LLDPE, ONY / adhesive / aluminum-vaporized PET / adhesive / CPP, PET / adhesive / aluminum-vaporized PET / adhesive / ONY / adhesive / LLDPE, CPP / adhesive / ONY / adhesive / LLDPE, ONY / adhesive / aluminum-vaporized LLDPE, ONY / adhesive / aluminum-vaporized CPP, etc. The abbreviations used in the above layer structure are as follows: / : represents the layer boundary ONY: Biaxially oriented polyamide film PET: Stretched polyethylene terephthalate film LLDPE: Unstretched linear low-density polyethylene film CPP: Unstretched polypropylene film OPP: oriented polypropylene film PE: Extrusion laminate or unstretched low density polyethylene film Al: Aluminum foil EVOH: Ethylene-vinyl alcohol copolymer resin Adhesive: An adhesive layer that bonds films together Aluminum vapor deposition: Indicates that aluminum is vapor-deposited [Example]

[0092] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The films were evaluated using the following measurement methods. Unless otherwise specified, measurements were carried out in a measurement room at 23°C and a relative humidity of 65%.

[0093] (1) Haze value of film Measurement was carried out using a direct reading haze meter manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K7105. (2) Film thickness The film was divided into 10 equal parts in the TD direction (for narrow films, the division was made to ensure a width that would allow thickness measurement), and 10 100mm films were cut out in the MD direction, and conditioned for at least 2 hours in an environment at a temperature of 23°C and a relative humidity of 65%. The thickness of the center of each sample was measured using a thickness measuring device made by Tester Sangyo, and the average value was taken as the thickness.

[0094] (3) Biomass content of film The obtained film biomass content was determined by radiocarbon (C) as specified in ASTM D6866-16 Method B (AMS). 14 ) measurements were performed. (4) Heat shrinkage rate of film The heat shrinkage was measured according to the following formula in accordance with the dimensional change test method described in JIS C2318, except that the test temperature was 160°C and the heating time was 10 minutes. Heat shrinkage rate = [(length before treatment - length after treatment) / length before treatment] x 100 (%) (5) Impact strength of the film Measurements were made using a film impact tester manufactured by Toyo Seiki Seisakusho, Ltd. The measured values were converted to values per 15 μm thickness and expressed as J (joules) / 15 μm. (6) Dynamic friction coefficient of film The coefficient of dynamic friction between the outer surfaces of the film rolls was evaluated under the following conditions in accordance with JIS C2151. The test specimen size was 130 mm wide and 250 mm long, and the test speed was 150 mm / min.

[0095] (7) Pinhole resistance of film when bent The number of pinholes due to bending fatigue was measured using a Gelbo Flex Tester manufactured by Rigaku Kogyosha Co., Ltd., according to the following method. A polyester adhesive was applied to the film prepared in the examples, followed by dry lamination with a 40 μm-thick linear low-density polyethylene film (L-LDPE film: Toyobo Co., Ltd., L4102). The laminate film was then aged for three days at 40°C to produce a laminate film. The resulting laminate film was cut into a 12-inch x 8-inch piece and formed into a 3.5-inch diameter cylinder. One end of the cylindrical film was fixed to the fixed head of a Gelbo Flex Tester, and the other end was fixed to the movable head, with an initial gripping distance of 7 inches. The test piece was subjected to a 440° twist in the first 3.5 inches of the stroke, followed by a linear horizontal motion for the next 2.5 inches, at a rate of 40 times / min. The number of pinholes that appeared in the laminate film was counted. Measurements were performed at 1°C. The test film was placed on filter paper (Advantec, No. 50) with the L-LDPE film side facing down, and the four corners were secured with Scotch tape (registered trademark). Ink (Pilot ink (product number INK-350-Blue) diluted 5 times with pure water) was applied to the test film and spread over the entire surface using a rubber roller. After wiping off any excess ink, the test film was removed and the number of ink dots on the filter paper was counted.

[0096] (8) Film abrasion and pinhole resistance A friction test was carried out using a fastness tester (manufactured by Toyo Seiki Seisakusho) according to the following method, and the distance at which pinholes occurred was measured. A test sample was made by folding the same laminate film as that produced in the pinhole resistance evaluation above into quarters to sharpen the corners, and then rubbing it against the inside surface of cardboard using a fastness tester with an amplitude of 25 cm, an amplitude speed of 30 times / min, and a weight of 100 g. The cardboard used was K280 x P180 x K210 (AF) = (surface liner x core material x backing liner (type of flute)). The pinhole occurrence distance was calculated according to the following procedure: The longer the pinhole occurrence distance, the better the abrasion pinhole resistance. First, a friction test was conducted with an amplitude of 100 times and a distance of 2500 cm. If no pinholes were found, the friction test was conducted with an amplitude of 20 times and a distance increased by 500 cm. If no pinholes were found, the friction test was conducted with an amplitude of 20 times and a distance increased by 500 cm. This process was repeated, and the distance at which a pinhole appeared was marked with an "X" and assigned a level of 1. If a pinhole appeared at an amplitude of 100 times and a distance of 2500 cm, the friction test was conducted with an amplitude of 20 times and a distance reduced by 500 cm. If a pinhole appeared, the friction test was conducted with an amplitude of 20 times and a distance reduced by 500 cm. This process was repeated, and the distance at which no pinholes appeared was marked with a "O" and assigned a level of 1. Next, for level 2, if the final result in level 1 was ○, the number of amplitudes was increased by 20 and a friction test was conducted, and if no pinholes were formed, a ○ was marked, and if a pinhole was formed, an X was marked.If the final result in level 1 was ×, the number of amplitudes was decreased by 20 and a friction test was conducted, and if no pinholes were formed, a ○ was marked, and if a pinhole was formed, an X was marked. Further, for levels 3 to 20, if the previous level was marked with an O, increase the number of amplitudes by 20 and conduct a friction test; if no pinholes appear, mark with an O; if pinholes appear, mark with an X. If the previous level was marked with an X, decrease the number of amplitudes by 20 and conduct a friction test; if no pinholes appear, mark with an O; if pinholes appear, mark with an X. Repeat this process and mark levels 3 to 20 with an O or X. For example, the results obtained are shown in Table 1. Using Table 1 as an example, we will explain how to determine the pinhole occurrence distance. Count the number of trials that are correct and incorrect for each distance. The distance with the most tests was used as the median, and the coefficient was set to 0. For distances longer than that, the coefficient was set to +1, +2, or +3 for every 500 cm, and for distances shorter than that, the coefficient was set to -1, -2, or -3 for every 500 cm. For all tests from levels 1 to 20, the number of tests in which no holes were formed was compared with the number of tests in which holes were formed, and the friction pinhole occurrence distance was calculated using the following formula for cases A and B. A: In all tests, the number of tests without holes is equal to or greater than the number of tests with holes. Distance at which friction pinholes occur = median + 500 x (Σ (coefficient x number of tests where no holes occurred) / number of tests where no holes occurred) + 1 / 2) B: In all tests, the number of tests without holes is less than the number of tests with holes. Distance at which friction pinholes occur = Median + 500 x (Σ (Coefficient x Number of tests with holes) / Number of tests with holes) - 1 / 2)

[0097] [Table 1]

[0098] (9) Lamination strength with polyethylene sealant A laminate film prepared in the same manner as described in the evaluation of pinhole resistance was cut into strips measuring 15 mm wide x 200 mm long. One end of the laminate film was peeled off at the interface between the biaxially oriented polyamide film and the linear low-density polyethylene film. Using an autograph (manufactured by Shimadzu Corporation), the laminate strength was measured three times in each of the MD and TD directions under the conditions of a temperature of 23°C, a relative humidity of 50%, a pulling speed of 200 mm / min, and a peel angle of 90°, and the average value was used to evaluate the laminate strength.

[0099] (10) Film formation stability during casting The molten resin was extruded from a T-die into a film, cast onto a cooling roll and cooled to obtain an unstretched film. The process was visually observed, and the film-forming stability was evaluated as follows. A: The film formation was stable and a uniform unstretched film was obtained. B: Film formation was a little unstable, and fluctuations were observed in the width of the unstretched film, but biaxial stretching was possible. C: The film formation was unstable and the unstretched film was inhomogeneous, so a biaxially stretched film could not be obtained. Furthermore, a rating of B or higher indicates practicality. (11) Generation period of thermal degradation products formed at the die lip exit After cleaning the lip of the die, film production was started, and the time until thermal degradation products appeared on the lip of the die was observed.

[0100] (12) Relative viscosity of raw polyamide 0.25 g of polyamide was dissolved in 96% sulfuric acid in a 25 ml measuring flask to a concentration of 1.0 g / dl, and the relative viscosity of the resulting polyamide solution was measured at 20°C. (13) Melting point of raw polyamide Measurement was carried out in accordance with JIS K7121 using a differential scanning calorimeter, model SSC5200, manufactured by Seiko Instruments Inc., in a nitrogen atmosphere with a sample weight of 10 mg, a temperature rise starting temperature of 30°C, and a temperature rise rate of 20°C / min, and the endothermic peak temperature (Tmp) was determined as the melting point.

[0101] [Polyamide 6] The polyamide 6 used in the examples and comparative examples is as follows. Polyamide 6(a-1) Relative viscosity 2.8, melting point 220℃, manufactured by Toyobo Co., Ltd.

[0102] Polyamide 6 (a-2) obtained by chemical recycling Relative viscosity 2.7, melting point 221℃ Polyamide 6 fiber recovered from waste materials and a 75% by mass aqueous solution of phosphoric acid, a depolymerization catalyst, were placed in a depolymerization reactor and heated to 260°C under a nitrogen atmosphere. The reaction was initiated by blowing superheated steam into the depolymerization reactor, and the ε-caprolactam and water vapor continuously distilled from the depolymerization reactor were cooled and the ε-caprolactam distillate was collected. The collected distillate was concentrated in an evaporator, and the resulting ε-caprolactam was repolymerized to obtain chemically recycled polyamide resin.

[0103] Polyamide 6 (a-3) obtained by mechanical recycling Relative viscosity 2.6, melting point 221℃ The non-standard film and scrap materials (edge trimmings) generated from the stretched film produced in Example 1 were collected and crushed, kneaded in an extruder at a cylinder temperature of 270°C, pelletized, and then dried at 100°C under reduced pressure to obtain mechanically recycled polyamide 6.

[0104] [Example 1-1] Using an apparatus consisting of an extruder and a 380 mm wide T-die, the following molten resin composition was extruded from the T-die into a film, which was then cast onto a cooling roll controlled to a temperature of 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 200 μm. (Resin composition) Polyamide 6 (a-1): 92 parts by mass Polyamide 6 (a-2): 5 parts by mass Polyamide 11 (manufactured by Arkema, relative viscosity 2.5, melting point 186°C): 3 parts by mass Porous silica microparticles (manufactured by Fuji Silysia Chemical Ltd., average particle size 2.0 μm, pore volume 1.6 ml / g): 0.45% by mass Fatty acid bisamide (ethylene bisstearic acid amide manufactured by Kyoeisha Chemical Co., Ltd.): 0.15% by mass

[0105] The resulting unstretched film was fed into a roll-type stretching machine and stretched 1.73 times in the MD direction at 80°C using the differential speed of the rolls, followed by a further stretch of 1.85 times at 70°C. This uniaxially stretched film was then continuously fed into a tenter-type stretching machine, preheated at 110°C, and stretched 1.2 times in the TD direction at 120°C, 1.7 times at 130°C, and 2.0 times at 160°C. It was then heat-set at 218°C and relaxed 7% at 200°C. The surface to be dry-laminated with a linear low-density polyethylene film was then corona-discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the resulting biaxially stretched film are shown in Table 2.

[0106] [Examples 1-2 to 1-12] A biaxially stretched film was obtained in the same manner as in Example 1-1, except that the raw material resin composition and film-forming conditions such as the heat setting temperature were changed as shown in Table 2. The evaluation results of the obtained biaxially stretched film are also shown in Table 2. In the examples and comparative examples, the following polyamide resins at least part of which are derived from biomass were used as raw materials. Polyamide 410: (DSM, ECOPaXX Q150-E, melting point 250°C) Polyamide 610: (Arkema, RilsanS SMNO, melting point 222°C) Polyamide 1010: (Arkema, Rilsan™ TMNO, melting point 202°C)

[0107] [Table 2A]

[0108] [Table 2B]

[0109] As shown in Table 2, the films obtained in the examples had both good flex pinhole resistance and good abrasion pinhole resistance. In addition, the films had low haze, good transparency, high impact strength, and high lamination strength with sealant films, making them excellent as packaging films.

[0110] [Comparative Examples 1-1 to 1-5] A biaxially stretched film was obtained in the same manner as in Example 1-1, except that the raw material resin composition and film-forming conditions such as the heat setting temperature were changed as shown in Table 3. The evaluation results of the obtained biaxially stretched film are shown in Table 3. However, in Comparative Example 1-4, the molten resin could not be stably extruded from the T-die into a film shape, and a homogeneous unstretched film could not be obtained, so biaxial stretching was not possible.

[0111] [Table 3]

[0112] As shown in Table 3, the biaxially oriented polyamide films of Comparative Examples 1-1 and 1-2, which did not contain a material for improving pinhole resistance, and the biaxially oriented polyamide film of Comparative Example 1-3, which contained too little polyamide 11, had poor pinhole resistance. In Comparative Example 1-4, the polyamide 11 content was too high, so the molten resin could not be stably extruded into a film from the T-die, resulting in a homogeneous unstretched film and no biaxially oriented polyamide film. In Comparative Example 1-5, a polyamide elastomer conventionally used as a material for improving pinhole resistance was used. Although the pinhole resistance was good, the abrasion pinhole resistance was poor. Furthermore, there was a drawback in that degraded materials were easily attached to the die during long-term production, making long-term continuous production impossible.

[0113] [Example 2-1] Using an apparatus consisting of two extruders and a 380 mm wide coextrusion T-die, layers were laminated in a B layer / A layer / B layer configuration using the feedblock method, and the molten resin was extruded from the T-die into a film, which was then cast onto a cooling roll controlled at 20°C and electrostatically adhered to obtain an unstretched film with a thickness of 200 μm. The feedblock configuration and extruder output were adjusted so that the thickness of the biaxially oriented polyamide film was 15 μm in total, with the base layer (A layer) being 12 μm thick and the front and back surface layers (B layers) being 1.5 μm thick each.

[0114] The resin compositions of the A layer and the B layer used in Example 2 were as follows. (Resin composition constituting layer A) Polyamide 6 (a-1): 92 parts by mass Chemically recycled polyamide 6 (a-2): 5 parts by mass Polyamide 11 (manufactured by Shuseisha, relative viscosity 2.5, melting point 186°C): 3 parts by mass (Resin composition constituting layer B) Polyamide 6 (a-1): 90 parts by mass Chemically recycled polyamide 6 (a-2): 5 parts by mass Polyamide MXD6 (manufactured by Mitsubishi Gas Chemical Co., Ltd., relative viscosity 2.1, melting point 237°C): 5 parts by mass Porous silica microparticles (manufactured by Fuji Silysia Chemical Ltd., average particle size 2.0 μm, pore volume 1.6 ml / g): 0.54 mass% Fatty acid bisamide (ethylene bisstearic acid amide manufactured by Kyoeisha Chemical Co., Ltd.): 0.15% by mass

[0115] The resulting unstretched film was fed into a roll-type stretching machine and stretched 1.73 times in the MD direction at 80°C using the differential speed of the rolls, followed by a further stretch of 1.85 times at 70°C. This uniaxially stretched film was then continuously fed into a tenter-type stretching machine, preheated at 110°C, stretched 1.2 times in the TD direction at 120°C, 1.7 times at 130°C, and 2.0 times at 160°C. It was then heat-set at 218°C and relaxed 7% at 218°C. The surface to be dry-laminated with a linear low-density polyethylene film was then corona-discharge-treated to obtain a biaxially stretched polyamide film. The evaluation results of the resulting biaxially stretched film are shown in Table 4.

[0116] [Examples 2-2 to 2-12] A biaxially stretched film was obtained in the same manner as in Example 2-1, except that the film-forming conditions, such as the resin compositions of Layer A and Layer B and the heat setting temperature, were changed as shown in Table 4. The evaluation results of the obtained biaxially stretched film are also shown in Table 4.

[0117] [Table 4A]

[0118] [Table 4B]

[0119] As shown in Table 4, the films obtained in the examples had both good flex pinhole resistance and good abrasion pinhole resistance. In addition, the films had low haze, good transparency, high impact strength, and high lamination strength with the sealant film, making them excellent as packaging films.

[0120] [Comparative Examples 2-1 to 2-7] A biaxially stretched film was obtained in the same manner as in Example 2-1, except that the film-forming conditions, such as the resin compositions of Layer A and Layer B and the heat setting temperature, were changed as shown in Table 5. The evaluation results of the obtained biaxially stretched film are also shown in Table 5. However, in Comparative Example 2-4, the molten resin could not be stably extruded from the T-die into a film shape, and a homogeneous unstretched film could not be obtained, so biaxial stretching was not possible.

[0121] [Table 5] The biaxially stretched polyamide films of Comparative Examples 2-1 and 2-2, which did not contain a material for improving pinhole resistance, and the biaxially stretched polyamide film of Comparative Example 2-3, which contained too little polyamide 11, exhibited poor pinhole resistance. In Comparative Example 2-4, the polyamide 11 content was too high, so the molten resin could not be stably extruded into a film from the T-die, resulting in a homogeneous unstretched film and no biaxially stretched polyamide film. In Comparative Example 2-5, the thickness and thickness ratio of Layer A were small, resulting in poor pinhole resistance. In Comparative Example 2-6, the amount of polyamide MXD6 in Layer B was high and the amount of polyamide 6 resin was low, resulting in poor pinhole resistance and abrasion resistance. In Comparative Example 2-7, a polyamide elastomer conventionally used as a material for improving pinhole resistance was used, resulting in good pinhole resistance but poor abrasion resistance. Furthermore, there was a drawback in that deterioration materials tended to adhere to the die during long-term production, making it impossible to carry out long-term continuous production.

[0122] [Examples 3 and 4] The biaxially stretched polyamide films produced in Examples 1-2 and 2-2 were used to produce laminate films with the following configurations (1) to (9), and three-side seal type and pillow type packaging bags were produced using the laminate films (1) to (9). Packaging bags with good appearance and resistance to tearing in a drop impact test were produced. (1) Biaxially oriented polyamide film layer / printing layer / polyurethane adhesive layer / linear low-density polyethylene film sealant layer (2) Biaxially oriented polyamide film layer / printing layer / polyurethane adhesive layer / unstretched polypropylene film sealant layer (3) Biaxially oriented PET film layer / printing layer / polyurethane adhesive layer / biaxially oriented polyamide film layer / polyurethane adhesive layer / unstretched polypropylene film sealant layer (4) Biaxially oriented PET film layer / printing layer / polyurethane adhesive layer / biaxially oriented polyamide film layer / polyurethane adhesive layer / linear low-density polyethylene film sealant layer (5) Biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / inorganic thin film protective layer / printing layer / polyurethane adhesive layer / linear low-density polyethylene film sealant layer (6) Linear low-density polyethylene film sealant layer / polyurethane adhesive layer / biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / polyurethane adhesive layer / linear low-density polyethylene film sealant layer (7) Linear low-density polyethylene film layer / polyurethane adhesive layer / biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / polyurethane adhesive layer / linear low-density polyethylene film layer / low-density polyethylene / paper / low-density polyethylene / linear low-density polyethylene film sealant layer (8) Biaxially oriented polyamide film layer / anchor coat layer / inorganic thin film layer / inorganic thin film protective layer / printing layer / polyurethane adhesive layer / unstretched polypropylene film sealant layer (9) Biaxially oriented PET film layer / inorganic thin film layer / inorganic thin film protective layer / printing layer / polyurethane adhesive layer / biaxially oriented polyamide film layer / polyurethane adhesive layer / easy-peel type unstretched polypropylene film sealant layer [Industrial Applicability]

[0123] The biaxially oriented polyamide film of the present invention has excellent impact resistance, flexural pinhole resistance, and abrasion pinhole resistance, making it suitable for use as a packaging material, such as food packaging. Furthermore, since it uses a resin polymerized from raw materials derived from biomass that is originally found on land, it is a carbon-neutral film and has little impact on the increase or decrease of carbon dioxide on land, thereby reducing the environmental burden. Furthermore, since it contains polyamide 6 chemically recycled from waste polyamide products, it allows for the reuse of plastic products that would previously have been discarded, thereby reducing the environmental burden and contributing to a reduction in the amount of plastic waste generated. [Explanation of symbols]

[0124] 1: Head of fastness tester 2: Cardboard 3: Mount for holding samples 4: Film sample folded in four 5: Rubbing amplitude direction

Claims

1. The resin contains only a polyamide resin, and the polyamide resin contains only 70 to 99 mass% of polyamide 6 and 1 to 30 mass% of polyamide 11, at least a part of which is derived from biomass, A method for producing a biaxially oriented polyamide film for food packaging, wherein the polyamide 6 contains 5 to 95 parts by mass of polyamide 6 obtained by chemical recycling, and more than 0 part by mass but not more than 50 parts by mass of polyamide 6 obtained by mechanical recycling, based on 100 parts by mass of polyamide 6.

2. The radioactive carbon (C １４ 2. The method for producing a biaxially oriented polyamide film for food packaging according to claim 1, characterized in that the content of carbon derived from biomass as measured by JIS K 1001-2001 is 1 to 15%.

3. 3. A method for producing a biaxially oriented polyamide film for food packaging, in which one or more layers are laminated on both sides of a biaxially oriented polyamide film for food packaging obtained by the method for producing a biaxially oriented polyamide film for food packaging according to claim 1 or 2, wherein the laminated layers contain 70 to 100% by mass of polyamide 6, and the polyamide 6 contains 5 to 95 parts by mass of polyamide 6 obtained by chemical recycling, and more than 0 parts by mass but not more than 50 parts by mass of polyamide 6 obtained by mechanical recycling, based on 100 parts by mass of polyamide 6.

4. The method for producing a biaxially oriented polyamide film for food packaging according to claim 3, wherein the thickness of the laminated layer is 7 to 50% of the total thickness of the film.

5. A method for producing a biaxially oriented polyamide film for food packaging, characterized in that the biaxially oriented polyamide film for food packaging obtained by the method for producing a biaxially oriented polyamide film for food packaging according to any one of claims 1 to 4 satisfies the following (a) and (b): (a) The number of pinhole defects is 10 or less when a twisting and bending test using a Gelbo flex tester is performed 1,000 times at a temperature of 1°C, (b) The distance until pinholes appear in the friction pinhole resistance test is 2900 cm or more.

6. A method for producing a biaxially oriented polyamide film for food packaging, characterized in that the biaxially oriented polyamide film for food packaging obtained by the method for producing a biaxially oriented polyamide film for food packaging according to any one of claims 1 to 5 has a haze of 10% or less and a dynamic friction coefficient of 1.0 or less.

7. A method for producing a biaxially oriented polyamide film for food packaging, characterized in that the biaxially oriented polyamide film for food packaging obtained by the method for producing a biaxially oriented polyamide film for food packaging according to any one of claims 1 to 5 is bonded to a polyethylene sealant film, and the laminate strength after bonding is 4.0 N / 15 mm or more.

8. A method for producing a laminated film for food packaging, comprising laminating a sealant film on at least one side of a biaxially oriented polyamide film for food packaging obtained by the method for producing a biaxially oriented polyamide film for food packaging according to any one of claims 1 to 7.

9. A method for producing a packaging bag for packaging food, using the laminated film for packaging food obtained by the method for producing a laminated film for packaging food according to claim 8.

Images